Method and device for decentralized transmission of data on a transmission line

ABSTRACT

Every subscriber node connected to an optical fiber comprises an access unit with a directional coupler which is controlled via an output amplifier, an optoelectric converter being connected subsequent to the directional coupler. Packets run on the fiber. The first bit of the packets indicates whether it is an empty packet (shown by &#34;light&#34; or &#34;bright&#34;) or a data packet (shown by &#34;no light&#34; or &#34;dark&#34;). As soon as the node has prepared data for transmission in a buffer storage, a test is effected at each arriving packet as to whether or not it is an empty packet. For this purpose, the light of every first bit is guided to a L/I detector which carries out this test in a &#34;flying&#34; manner, while a no-light bit passes on to the outgoing fiber. If the L/I bit indicates a data packet, the control immediately switches the directional coupler to pass, so that the packet passes the node so as to be unchanged. On the other hand, if the L/I bit indicates an empty packet, the contents of the buffer storage is read into this packet. The node cane accordingly transmit without the slightest time delay occurring in the packet stream.

BACKGROUND OF THE INVENTION

a) Field of the Present Invention

The invention is directed to a method and an assigned device fordecentralized transmission of data on a transmission line correspondingto the preamble of the independent claims.

b) Background Prior Art

Transmission lines and diverse types of data transmission via such linesare generally known. Recently, optical transmission lines have becomeincreasingly important for various reasons. In addition to the opticalpoint-to-point connections, there are also complicated networkstructures with optical lines. For example, in an article entitled"Optical fibres in local area networks", Communications/CommunicationsInternational, October 1985, pages 19 ff., B. Viklund describes variousnetwork structures with glass fiber cables for distribution networks andfor networks with connections between different subscribers which can beset up individually. In the latter, a ring configuration is mostfavorable. The subscriber stations of an optical transmission line ofthe aforementioned type are connected to the respective utilized fibersvia optical couplers.

At present, there are couplers, switches and modulators based on GaAssemiconductor material for optical systems which utilize electro-opticaleffects for influencing light. These elements work up to frequencies inthe gigahertz range.

The use of address-coded packets for transmitting data is generallyknown. Such packets comprise a head part (header) and a data part,wherein the head part contains all necessary data for the respectivepacket and the participating transmission devices, particularly therespective transmitter and receiver. The data part is available for thedata to be transmitted. If it is empty, it is referred to as an emptypacket.

Various methods are known for producing address-coded packets andconverting empty packets into data packets. In this respect, referenceis made e.g. to the patent CH 550 521 which describes one of the firstmethods presently known as "buffer insertion". What all of these methodshave in common is that they have a delay at some point, be it a matterof the insertion of a new packet into an existing stream of packets,wherein the entire stream is delayed by the length of a packet, or be ita matter of having to wait for the reading of the head part of a packetbefore it is clear whether or not it is an empty packet, etc.

In optical systems, a controlled delay on the transmission lines was(until now) not possible. Such a delay can only be effected in that itis effected in the electronic part of the system, e.g. by means of ashift register. In an optical transmission line chiefly comprisingso-called passive subscriber nodes which have no active light source(e.g. a laser diode), there is the problem of providing a method fordetecting passing empty packets entirely without delay and filling themwith prepared data. These methods must be consistent with the method ofreceiving data packets which run or arrive via the same transmissionline.

The solution to this problem is provided by means of the independentclaims, while the dependent claim indicates a construction of theinvention. Accordingly, it is now possible to set up relatively simpleand accordingly inexpensive subscriber nodes in optical transmissionlines.

The invention is explained in more detail in the following by way ofexample with the aid of seven diagrams.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of an optical transmission line;

FIGS. 2 and 3 show variants of the transmission line;

FIG. 4 is a schematic view of an optical directional coupler;

FIG. 5 is a symbolic view of the directional coupler;

FIG. 6 shows a schematic construction of a packet;

FIG. 7 is a block wiring diagram of a subscriber node.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a schematic view of a transmission line 10 on which digitalsignals are transmitted in the direction of the arrow. An optical fiber11, particularly a single-mode fiber, serves as transmission medium. Aplurality of subscriber nodes 12 is included in this fiber 11, so thatthe fiber 11 is divided into portions, but the light flow, as a whole,is not interrupted.

The light flow commences in a light source 16, particularly asemiconductor laser, which feeds a substantially continuous constantlight flow into the commencement of the fiber 11. The light flow ends inan optical receiver 18, particularly a photodiode with an amplifierconnected subsequently. The subscriber nodes 12 comprise access units 13which do not interrupt the light flow along the transmission lines 10 asdescribed. The subscriber nodes 12 are further constructed in such a waythat they can receive data contained in the light flow and insert datainto the light flow. For this purpose, an electronic receiver 23 whichprocesses the received data and a transmitter 25 which provides the datato be transmitted are connected to the access units 13.

FIG. 2 shows a first variant of the transmission line 10. The latter hasa ring-shaped configuration, so that the optical receiver 18 can beconnected, via a short electrical connection, to a transmitter 25 of astart-access unit 13 connected subsequent to the light source 16.Accordingly, a ring-shaped arrangement is formed in which everysubscriber node 12 can communicate with every other subscriber node 12.In so doing, the unit 16 forms the single light source.

FIG. 3 shows a second variant of the transmission line 10. In the case,the optical receiver 18 is connected to a transmitter 25' of anothertransmission line 10', likewise by means of a short electricalconnection. Similarly, this transmitter 25' is assigned to anotherstart-access unit 13' which is connected subsequent to another lightsource 16'. In this way, two or more transmission lines 10, 10' areswitchable in series: naturally, the transmission lines 10, 10' can inturn be combined in a circular manner in their entirety.

FIG. 4 shows a schematic, greatly enlarged view of an integrated opticaldirectional coupler 30 as the core of the aforementioned access units13. The directional coupler 30 comprises two adjacent optical ribbedwaveguides 34, 35 on an InP substrate 32, which ribbed waveguides 34, 35are covered by a total of four metallic control electrodes 36 to 39, viawhich electrical control voltage can be applied. The directional coupleris connected on its input side to an incoming fiber, particularly asingle-mode fiber 41, with one ribbed waveguide 34. It is connected onthe output side to an outgoing single-mode fiber 42 and 43 by the tworibbed waveguides 34, 35, respectively.

The described directional coupler 30, known per se, works as a lightswitch, wherein the light flow arriving via the fiber 41 can be dividedinto the two outgoing fibers 32, 43 more or less intensity dependingupon the voltages applied to the control electrodes 36 to 39. FIG. 5shows a symbolic view of the directional coupler 30 which is supposed toexpress the switching function. The arrow 44 symbolizes the electricalcontrol possibility which is provided via the control electrodes 36 to39 (FIG. 4).

FIG. 6 a schematic view of a sequence of digital packets 45 running onthe transmission line 10 with respect to time in the direction of thearrow. These packets are formed by means of intensity modulation of theconstant light flow generated by the light source 16 and comprise a headpart 46 and a data part 47 in each instance. If the data part 47 isempty, then it is an empty packet, otherwise it is a data packet. Thepackets 45 follow one another contiguously and in whatever successionand comprise a considerable quantity of bits, e.g. 1000 bits. Thepackets 45 are formed in such a way that every access unit 13 can besynchronized independently to the bit timing BT and the packet timing PTof the packets 45. The first bit of each packet 45 distinguishes theempty packets from the data packets and is designated L/I bit 48 in thefollowing (L=empty, I=data).

The packets 45 successively pass through all subscriber nodes 12 on thetransmission line 10. In so doing, the light intensity of the packets(which carries the data) diminishes because of losses in the opticalfibers 11 on the one hand and because of branching losses in the accessunits 13 on the other hand. These branch losses are unavoidable becauseevery receiver 23 continuously monitors all of the packets 45 passingthrough the respective access unit 13 to determine whether its addressis contained in the head part and consequently whether it (the receiver23) is accordingly the receiver of the respective data part 47determined by the address.

If data is to be transmitted to the transmission line 10 by atransmitter 25, this data is prepared in packets and written into emptypackets as they pass through the respective subscriber nodes 12. Forthis purpose, on the one hand, the L/I bit 48 of every packet 45 must beread in the respective subscriber node 12 or the respective receiver 23.On the other hand, this L/I bit must be simultaneously changed from itsone state L (empty) to its second state I (data) insofar as an emptypacket is concerned. Successive subscriber nodes 12 in the signal streamcan then accordingly determine that there is no longer an empty packetin the sequence, but rather a data packet.

The process of the simultaneous reading and changing of the respectiveL/I bit 48 is effected in the following manner: every subscriber node 12and accordingly also the respective receiver 23 is synchronized to thebit timing BT and the packet timing PT. As soon as data has beenprepared to be written into an empty packet, the respective access unit13 extracts completely the light of every subsequent L/I bit 48 to theL/I detector 56 with the aid of its directional coupler 30 (FIG. 7). Ifthe quantity of this light is smaller than a predetermined thresholdamount, or if it is zero, this signifies the "data" state I. In thiscase, it is a data packet which may not be changed. The directionalcoupler 30 is therefore reset its normal position immediately, i.e.already for the second bit of the respective packet 45. The data packetwhich continues to run accordinqly comprises a L/I bit 48 which isformed from "zero light" so as to be practically unchanged, while therest of the packet comprises the original bits, i.e. dark and lightpatterns, so as to be completely unchanged.

On the other hand, if the light quantity of the L/I bit 48 is greaterthan the aforementioned threshold amount, this signifies the L state,i.e. empty. In this case, it is an empty packet which is to be filledimmediately with the prepared data by means of modulation in bit timingBT. The L/I bit 48 was already changed from "bright" to "dark" by meansof the aforementioned position of the directional coupler 30, so thatthe packet 45 which continues to run to the next access unit 13 is acomplete data packet which has not undergone any delay in theaforementioned subscriber node 12 or by means of the conversion process.

The preconditions for the described method are that the L/I bit 48 beforemost at the tip of the packets 45 and that its first state L (emptypacket) be shown as bright or as present light intensity, while itssecond state is not present light intensity.

FIG. 7 shows a refined block wiring diagram of a subscriber node 12 withthe described access unit 13 and the respective receiver 23 andtransmitter 25. This subscriber node 12 constitutes a technicaldevelopment by means of which the described method of simultaneousreading and conversion of the L/I bit 48 can be carried out. As alreadydescribed, an access unit 13 which comprises a directional coupler 30 isincluded in the optical fiber 11. An optoelectric converter 50 withintegrated input amplifier is connected to the output of the access unit13. An output or driver amplifier 51 is connected with the controlelectrodes 36 to 39 of the directional coupler 30 which (as explainedwith the aid of FIG. 5) are symbolized by the arrow 44.

The aforementioned receiver 23, a synchronizing unit 54 and a L/Idetector 56 are connected to the output of the input amplifier 50. Thereceiver 23 comprises a buffer storage 58 for receiving all bits ofreceived packets 45 and an actual receiver unit 59 for the reception ofthe data determined for the respective node 12. The synchronizing unit54 is a unit, known per se, which regenerates the bit timing BT and thepacket timing PT from the signal pattern on the fiber 11 synchronouslyand in correct phase. These timings BT and PT applied to their outputsserve for the control of the entire respective subscriber node 12.Finally, the L/I detector 56 is by its function already point of thesender 25. The L/I detector 56 indicates whether or not the L/I bit 48comprises the significance L (empty packet) or I (data packet). The L/Idetector 56 can be constructed e.g. as monostable multivibrator with afixed threshold voltage.

The transmitter 25 is connected prior to the output amplifier 51. Thetransmitter 25 comprises a buffer storage 68 in which the data to betransmitted is prepared in packets. In addition, it comprises an actualtransmitting unit 69 and a control 62 with two subordinate controls 62.1and 62.2. The control 62 is connected to the buffer storage 68, the L/Idetector 56 and the output amplifier 51 in accordance with the signals.

The subscriber node 12 operates as follows: as soon as data is preparedfor a packet 45 in the buffer storage 68, the control 62 iscorrespondingly informed via the connection 63. The subordinate control62.2 then extracts the light from every L/I bit 48 (and only the latter)arriving subsequently at the access unit 13 by means of a correspondingdirection control of the directional coupler 30 via the optoelectricconverter 50 to the L/I detector 56. This L/I detector 56 immediatelydecides whether or not the L/I bit 48 indicates the L state (emptypacket) or I state (data packet). In the L state, the subordinatecontrol 62.1 immediately sends a transmit command to the buffer storage68 via the connection 64, whereupon the buffer storage 68 via the outputamplifier 51 transmits the data contained with it to the respectiveempty packet in bit timing BT. This means that the light flow of theempty packet becomes modulated and the packet is transformed into a datapacket. On the other hand, if the L/I bit 48 indicates a data packet I,nothing more happens, since the subordinate control 62.2 switches thedirectional coupler 31 back into its pass direction and accordingly intothe basic state, generally after every L/I bit 38. The respective datapacket can therefore pass unchanged. In this way, the next empty packetafter the indicated ready-to-transmit state is filled with data, whilethe data packets pass in an unimpeded manner.

The described optical transmission line 10, 10' with its subscribernodes 12 is suitable for transmission frequencies up to the gigahertzrange. Preferably, ring networks can be constructed, in which everysubscriber node 12 can communicate with every other node as desired. Thelength between two respective light sources can amount to manykilometers. It depends solely on the losses in the optical fibers 11 andon the quantity of the respective connected subscriber nodes 12, sincethere (as described) cause a certain light loss too.

While the foregoing description and drawings represent the preferredembodiments of the present invention, it will be obvious to thoseskilled in the art that various changes and modifications may be madetherein without departing from the true spirit and scope of the presentinvention.

What is claimed is:
 1. In a method for decentralized transmission ofdata on an optical transmission line from a plurality of subscribernodes, wherein the data is prepared in packets in the subscriber nodes,the packets having a beginning and an ending bit, wherein data packetsand empty packets immediately follow one another on the transmissionline in random order and the data is carried by means of a modulatedlight flow, wherein every subscriber node is synchronized to the bittiming of the transmission line, and wherein data packets and emptypackets are distinguished by the significance of a L/I bit in such a waythat the L/I bit's first state (L) signifies an empty packet and the L/Ibit's second state (I) signifies a data packet, the improvementcomprising: arranging the L/I bit as the beginning bit of the packets,and simultaneously:(a) determining the initial state (L,I) of the L/Ibit of every successively arriving packet, (b) bringing the L/I bit intothe second state (I) in every subscriber node which has prepared datafor transmission, (c) writing the prepared data in the packet whichoriginally had an L/I bit designating the first state to form a newpacket, and (d) transmitting the new packet to the next subscriber node.2. A method according to claim 1, including the steps of using lightoriginating from a constant light source on the transmission line, andwriting data into a packet by means of the intensity modulation of thelight.
 3. A method according to claim 2, wherein the intensitymodulation of the light is effected by means of the branching off of aportion of the respective intensity of a main path of the light to asecondary path.
 4. A method according to claim 1, wherein the firststate (L) of the L/I bit is constituted by absence of light intensityand the second state (I) by the light intensity.
 5. In a device forimplementing a method for decentralized transmission of data on anoptical transmission line from a plurality of subscriber nodes, whereinthe data is prepared in packets from a plurality of subscriber nodes,wherein data packets and empty packets successively follow one anotheron the transmission line in desired sequence and the data are carried bymeans of a modulated light flow, wherein every subscriber node issynchronized to the bit timing and the packet timing of the transmissionline, and wherein data packets and empty packets are distinguished bythe significance of a L/I bit in such a way that its first state (L)signifies an empty packet and its second state (I) signifies a datapacket, wherein every subscriber node comprises a directional couplerwhich is connected to an optical fiber and to which an optoelectricconverter is assigned, an input amplifier and an output amplifier fordriving the control electrodes of the directional coupler, asynchronizing unit for synchronizing the respective subscriber node tothe bit timing and packet timing at the directional coupler, and abuffer storage in which the data to be transmitted can be prepared, theimprovement comprising: every subscriber node including a first control,which extracts the total light intensity form the L/I bit transmitted bythe optical fiber and routes it to the optoelectric converter via theoutput amplifier and the directional coupler; a L/I detector fordetermining the respective initial state (L,I) of the L/I bits and fortransmitting a signal which corresponds to the state of the L/I bit, theL/I detector being connected subsequent to the optoelectric converter;and a second control which triggers the transmission of the dataprepared in the buffer storage in the packet which originally had an L/Ibit which designates the empty state.
 6. A device according to claim 5,wherein the L/I detector is a monostable multivibrator with fixedthreshold voltage.
 7. In a method for decentralized transmission of dataon an optical transmission line from a plurality of subscriber nodes,wherein the data is prepared in packets in the subscriber nodes, thepackets having a beginning and an ending bit, wherein data packets andempty packets immediately follow one another on the transmission line inrandom order and the data is carried by means of a modulated light flow,wherein every subscriber node is synchronized to the bit timing of thetransmission line, and wherein data packets and empty packets aredistinguished by the significance of a L/I bit in such a way that theL/I bit's second state (L) signifies an empty packet and the L/I bit'ssecond state (I) signifies a data packet, the improvement comprising:using light originating from a constant light source on the transmissionline, arranging the L/I bit as the beginning bit of the packets, andsimultaneously:(a) determining the initial state (L,I) of the L/I bit ofevery successively arriving packet; (b) brining the L/I bit into thesecond state (I) in every subscriber node which has prepared data fortransmission, (c) writing the prepared data by means of intensitymodulation of the light into the packet which originally had an L/I bitdesignating the first state (L), and (d) transmitting the packet to thenext subscriber node.
 8. A method according to claim 7, wherein theintensity modulation of the light is effected by means of the branchingoff of a portion of the respective intensity of a main path of the lightto a secondary path.
 9. A telecommunications network for thetransmission of information packets which comprise bits of information,said telecommunications network comprising:a single optical fiber; asingle light source for delivering a constant light beam at one end ofsaid fiber, said light beam having a fixed bit rate and a fixed packetrate; and, a plurality of subscriber nodes connected to said fiber, eachof said nodes comprising a modulator for intensity modulation of saidlight beam for forming said information packets, said informationpackets having a full/empty bit which designates whether an individualpacket is full or empty, said full/empty bit being a first bit of saidinformation packets, and wherein said subscriber nodes are synchronizedwith said bit rate and said packet rate to accept and transmitinformation without delay, said fiber transporting digital data betweensaid subscriber nodes, wherein said nodes transmit data by searching andwaiting for an empty packet to arrive, having found said empty packet,filling said packet to form a full packet, said full packet beingtransmitted and said nodes having means for effecting a reading processwhich changes said full/empty bit to designate its corresponding datapacket as said full packet.
 10. The telecommunications network accordingto claim 9, wherein said modulator is a directional coupler, and saidintensity modulation is effected by branching off a portion of therespective intensity of said light beam of said fiber to a secondarylight path.
 11. The telecommunications network according to claim 10,wherein said subscriber nodes further comprise:an optoelectronicconverter connected to said secondary light path; a buffer storage forinformation to be transmitted; a first and a second control unit tocontrol said directional coupler via an output amplifier; and, afull/empty-detector connected to said optoelectronic converter and tosaid control units, wherein said second control unit causes said lightintensity travelling within said fiber at said full/empty bit to branchoff to said secondary path causing said full/empty bit to indicate thatsaid packet is full, and if said full/empty-bit originally indicatedthat said packets was empty, said first empty packet to contain saidinformation of said buffer storage.
 12. The telecommunications networkaccording to claim 11, wherein said full/empty-detector is a monostablemultivibrator with fixed threshold voltage.